1. Field of Utilization in Industry
This invention relates to a bobbin for a multiple-connected inductor used mainly in the case of constituting a delay line or a filter, and such that coils are separately wound over a plurality of sections.
2. Prior Art
For a bobbin for a multiple-connected inductor of this kind, it is important to precisely set inductance values of respective coils wound thereon and an electromagnetic coupling between coils.
Bobbins are ordinarily formed by sintered ferrite or synthetic resin. Under the present state where bobbins are considerably being miniaturized, when an example of a square flange is taken, since one side of the square flange is 4 mm or less, and the thickness of the flange and/or the width of the winding groove between flanges is 3 mm or less, it difficult to mold, with good yield, by using ferrite, an elongated bobbin in a uniaxial form in which flanges and winding groove are continuous to each other. The trouble that the flange may be partially broken is apt to occur. Further, since the coupling between coils becomes strong, the adjustment of the coupling is difficult.
In the case of synthetic resin, molding is easy, but it is unable to increase the inductance of the coil. A rod-shaped core may be embedded within the synthetic resin. However, since it is difficult to precisely determine the position of the core within the synthetic resin, unevenness in inductance or coupling between coils is apt to occur.